A hands-free device for a vehicle, which enables a driver to communicate with another person using a speaker of a vehicle audio system and a microphone installed in a passenger compartment, has been known. By using the hands-free device, a driver can talk with another person without holding a cell phone in his hand.
In general, a driver needs to pay more attention when turning at a traffic intersection, changing a lane and the like than when driving straight ahead. In such a situation, it may be difficult to communicate safely even using the hands-free device.
For example, JP2008-82940A describes a navigation system that estimates a workload (e.g., perception load) of a driver based on a scheduled travel route of a vehicle and provides the driver with various information at a timing where the workload is low. Such a system may be employed to a hands-free device mounted in a vehicle. If a cell phone has an incoming call while the driver's workload is high, that is, while the driver is in a driving situation paying more attention, it may be possible to delay a ring alert until the driver's workload becomes low. Thus, the driver may talk through a cell phone using the hands-free device in a good time where the workload is low.
In such a case, however, if a phone call is made from a cell phone of another driver (e.g., transmitting driver) who is driving another vehicle, the timing of ringing a ring alert is determined without considering a workload of the transmitting driver. Therefore, the transmitting driver may not talk in a good time.